1. Field of the Invention
The present invention relates in general to stacked integrated circuit (IC) dice, and, in particular, to devices and methods for stacking wire-bonded IC dice on flip-chip bonded IC dice.
2. State of the Art
Integrated circuit (IC) dice or xe2x80x9cchipsxe2x80x9d are small, generally rectangular IC devices cut from a semiconductor wafer, such as a silicon wafer, on which multiple IC""s have been fabricated. Traditionally, bare IC dice are packaged to protect them from corrosion by enclosing them in die packages. Such packages work well to protect IC dice, but they can be more bulky than desirable for certain multi-chip applications requiring compact die packaging.
Accordingly, a variety of compact die packaging techniques exists. In one such technique, the back-side surface of a bare IC die is directly mounted on the surface of a Printed Circuit Board (PCB), and bond pads on the front-side surface of the bare die are then wire-bonded to wire-bondable pads on the surface of the PCB to interconnect circuitry in the die with external circuitry through conductive traces on the PCB. This technique may be referred to as xe2x80x9cChip-On-Board (COB) with wire-bonding.xe2x80x9d In another such technique, conductive xe2x80x9cbumpsxe2x80x9d on the front-side surface of a bare IC die are bonded to xe2x80x9cflip-chipxe2x80x9d pads on the surface of a PCB to interconnect circuitry in the die with external circuitry. Both the COB with wire-bonding technique and the flip-chip technique are well-known to those of skill in the field of this invention, and are described in more detail in U.S. Pat. Nos 5,422,435, 5,495,398, 5,502,289, and 5,508,561.
While these traditional compact die packaging techniques are more compact than the bulky die packages described above, they still are not compact enough for some multi-chip applications requiring many chips in a small area. For example, an ever-growing demand for Dynamic Random Access Memory (DRAM) capacity is driving a need for ever-more DRAM memory chips to be packed into a small area.
As a consequence, a variety of techniques exists for stacking chips on top of one another to increase the number of chips provided in a small area. As described in U.S. Pat. Nos. 5,228,192, 5,252,857, and 5,514,907, some of these techniques involve mounting individual bare IC dice, or individual dice packaged using a traditional die package, to parts of a structure, and then assembling the structure so the mounted dice are stacked. Also, as described in U.S. Pat. No. 5,323,060, another technique involves stacking bare IC dice on top of one another, and then wire-bonding the dice to a PCB and to one another. Similarly, as described in U.S. Pat. No. 5,399,898, a further technique involves stacking exotic IC dice having conductive bumps or pads on both sides on top of one another and then flip-chip bonding the dice to a PCB and to one another. Further, as described in U.S. Pat. Nos. 5,422,435, 5,495,398, and 5,502,289, an additional technique involves stacking bare IC dice on top of a die mounted to a PCB using the COB with the wire-bonding technique described above. These stacked dice are then wire-bonded to the PCB and to one another, or are interconnected using flip-chip bumps, or both. In addition, as described in U.S. Pat. No. 5,527,740, a still further technique involves back-side bonding a pair of IC dice to one another and then wire-bonding bond pads on the front-sides of the bonded dice to a PCB.
While all of these stacking techniques work well to increase the density of chips provided in a given area, they do not provide a simple stacking technique for IC dice flip-chip mounted to a PCB in the manner described above. They also do not provide a stacking technique that can be used to repair or replace a defective IC die flip-chip mounted to a PCB. Such xe2x80x9crepairxe2x80x9d stacking techniques are well known for IC dice mounted to a PCB using the COB with wire-bonding technique, as described in U.S. Pat. No. 4,567,643.
Therefore, there is a need in the art for a simple stacking technique for IC dice flip-chip mounted to a PCB or any other base, and the inventive technique should be useful for repairing or replacing flip-chip mounted IC dice.
An inventive electronic device, such as a multi-chip module (MCM), a Single In-line Memory Module (SIMM), or a Dual In-line Memory Module (DIMM), includes a base, such as a printed circuit board, having a surface on which flip-chip pads and wire-bondable pads are provided. The flip-chip pads define an area on the surface of the base at least partially bounded by the wire-bondable pads. A first integrated circuit (IC) die is flip-chip bonded to the flip-chip pads, and a second IC die of the same type as the first die is back-side attached to the first IC die and then wire-bonded to the wire-bondable pads. As a result, the flip-chip mounted first IC die is stacked with the second IC die in a simple, novel manner. Because the first and second IC dice are of the same type, the flip-chip pads and the wire-bondable pads are interconnected so they xe2x80x9celectrically mirrorxe2x80x9d one another (i.e., so corresponding bond pads on the xe2x80x9cflippedxe2x80x9d first IC die and the second IC die are interconnected).
In another embodiment of the present invention, a memory device includes one or more electronic devices, as described above. In a further embodiment, an electronic system includes input, output, memory, and processor devices, and one of these devices includes a base, first IC die, and second IC die, as described above. In still further embodiments, the wire-bondable and flip-chip pads of the electronic device, described above, are interconnected in single and multiple layers of the base.
In an additional embodiment, an electronic device, as described above, also includes a third IC die back-side attached to the second IC die and then wire-bonded to the wire-bondable pads on the surface of the base. In a still additional embodiment, an electronic system includes input, output, memory, and processor devices, and one of these devices includes a base and first, second, and third IC dice, as described above.
In still another embodiment, a base has a surface on which flip-chip pads are arranged in a pattern. The flip-chip pads are flip-chip connectable to flip-chip bumps on a first IC die carryable on the surface. Wire-bondable pads are interconnected with the flip-chip pads and are arranged in a pattern on the surface so the wire-bondable pads as a group xe2x80x9celectrically mirrorxe2x80x9d the flip-chip pads as a group. The wire-bondable pads at least partially bound an area defined by the pattern of flip-chip pads and are wire-bondable to bond pads on a second IC die carryable on the first IC die. An additional embodiment is a method of making a base, as described above.
In yet another embodiment, an electronic system includes input, output, memory, and processor devices, and one of these devices includes a base, as described above.
In an additional embodiment, a method of assembling a multi-chip structure on a base having a surface for carrying the structure includes: providing a plurality of flip-chip pads arranged in a pattern on the surface of the base defining an area thereon; providing a plurality of wire-bondable pads arranged in a pattern on the surface of the base and at least partially bounding the area defined by the pattern of flip-chip pads; interconnecting the wire-bondable pads and the flip-chip pads so the wire-bondable pads as a group electrically mirror the flip-chip pads as a group; positioning a first IC chip so a front-side surface thereof faces the surface of the base with a gap therebetween and with a plurality of flip-chip bumps on the front-side surface aligned with the flip-chip pads on the surface of the base; connecting the flip-chip bumps on the front-side surface of the first chip to the flip-chip pads on the surface of the base; sealing the gap between the front-side surface of the first chip and the surface of the base; positioning a second IC chip so a back-side surface thereof faces a back-side surface of the first chip; attaching the back-side surface of the second chip to the back-side surface of the first chip; connecting a plurality of bond pads on a front-side surface of the second chip to the wire-bondable pads on the surface of the base; and sealing the first and second chips.
In a further embodiment, a method of repairing an IC die having flip-chip bumps that are bonded to flip-chip pads on a surface of a die-carrying base, such as a printed circuit board, includes: providing wire-bondable pads on the surface of the base arranged generally about the perimeter of the flip-chip bonded die and each connected to one of a group of conductors through which the flip-chip bonded die communicates with circuitry external to the die; back-bonding a replacement IC die to the back-side surface of the flip-chip bonded IC die; disconnecting the flip-chip bonded IC die from the conductors; and wire-bonding bond pads on the replacement die to the wire-bondable pads on the surface of the base so the replacement die may communicate with circuitry external to the die.